1. Field of the Invention
The present invention related to a color mixing apparatus for reflective displays using a total internal reflection (TIR) prism, and more particularly, to a color mixing apparatus for reflective displays in which the magnitude of prism angle in the TIR prism and the magnitude of an incident angle of each color light is adjusted to facilitate the design of a projection lens.
2. Description of the Related Art
A color mixing apparatus for reflective displays using a TIR prism mixes R, G and B color light using three TIR prisms, three reflective display devices and a color cube. The mixed color light is formed as an image on a screen via a projection lens. As the F number of the projection lens (focal distance/lens effective aperture) become larger, the projection lens can be more easily designed. That is, if the F number of the projection lens is large, the number of the lenses used for designing the projection lens is reduced, thereby making it easy to design a projection lens. Thus, in order to enlarge the F number of the projection lens, the magnitude of the off-axial angle should be reduced or a back focal length (BFL) should be shortened in a color mixing apparatus.
However, in the color mixing apparatus, if the magnitude of the off-axial angle becomes smaller, the BFL becomes longer, while if the BFL becomes shorter, the magnitude of the off-axial angle becomes greater. Thus, it is difficult to reduce both the magnitude of the off-axial angle and the BFL.